This invention relates to a check valve formed integrally with a tubular flow conduit and a method of manufacturing the same, as distinguished from securing a separate check valve assembly to the flow conduit.
In many applications it is desirable to incorporate a check valve in a fluid flow conduit or line to prevent fluid from flowing in one direction while allowing fluid to flow in the other direction. In certain of those prior applications a check valve has been integrated directly in the fluid line, thereby avoiding the necessity of using self-contained separate valve assemblies that must be joined in an appropriate manner to the tubing or pipe system. In such integrated applications, cost savings have been realized by using the tubing itself as the casing or body portion of the check valve assembly that is thus integrated with the tube. Such integrated check valve assemblies also eliminate leakage points from seals because they avoid breaking the continuity of the tubing.
Prior examples of integrating a check valve into a length of tubing stock are disclosed in the expired U.S. Pat. No. 3,387,625 Laure and in the expired U.S. Pat. No. 4,611,374 Schnelle et al. Both of these prior art patents incorporate a ball-type check valve in a flow conduit made of material that is capable of being shaped or worked. The integral valve cage or chamber as well as valve seat thus are formed by reducing the diameter of the tubing at two spaced points to thereby form both ends of the valve cage. One end is thus necked down to serve as the valve seat for the ball. The other end is likewise necked down to serve as a retainer either for a valve spring assembled in the valve cage (Laure '625), or for a valve-ball-retainer comprising a series of circumferentially spaced inwardly extending ball-retaining indentations that hold the ball from release from the cage, while allowing fluid flow around the ball through the tube (Schnelle et al '374).
While the aforementioned integrated in-line check valve and flow tube assemblies provide the aforestated advantages of avoiding assembling a separate check valve assembly to the tube, they are disadvantageous from the standpoint of requiring the nominal tube diameter to be reduced by the necking down operation both upstream and downstream of the ball valve element of the check valve, thereby reducing the fluid flow capacity of the tubular flow line.